Dynamic loud speaker unit



'Feb zfi, 1935. FANGER 1,992,300

y DYNAMIC 1.0m) SPEAKER'UNIT I Original Filed Sept. 25, 1928 k v j f I32 g 35, E 34 T INVIENTOR Y krm xvi/77 r syww ATTORNEY Patented Feb. 26,1935 UNITED STATES DYNAMIC LOUD SPEAKER UNIT Herman J. Fanger, Oakland,Calif.

Original application September 25, 1928, Serial No. 308,152. Divided andthis application July 26, 1932, Serial No. 624,732

8 Claims.

This invention relates to devices for transforming signal carryingelectrical impulses into sound waves; and more particularly to a deviceemploying the dynamic principle whereby a movable conductor is actuatedin accordance with the signals to be reproduced.

' This application is a division of an application filed in my name onSeptember 25, 1928, Serial Number 308,152, now Patent No. 1,895,071,granted Jan. 24, 1933, entitled Dynamic loud speaker lmitn' Such unitsemploy a magnetic field, usually produced by the aid of a field coilsupplied with direct current. The magnetic circuit includes a small gapin which a coil or other conductor is movable, in such manner that themovement cuts the magnetic lines of force, When such a conductor issupplied with current carrying the impulses, this current reacts withthe transverse field to move the coil, and this movement can be used toactuate an air actuator, such as adiaphragm or a cone.

The field coil, in order to secure good efliciency, must be suppliedwith a considerable energizing 25 current, sometimes of the order of anampere.

In prior devices, the heat losses in the coil serves to heat the coiland the surrounding parts of the structure; and it is obvious that thisheating must be taken care of by proper circulation so that it 30 maynot affect the unit deleteriously.

It is one of the objects of my invention to prevent this undesirabletemperature rise, and more particularly by providing a large radiatingsurface for the structure. I accomplish this result 35 by so arrangingthe magnetic circuit that it has, in addition to an external radiatingsurface, a

supplemental interior radiating surface. Ac-' cordingly, it is anotherobject of my invention to provide a structure for the magnetic circuitthat accomplishes these useful results.

In a single coil device, it is evident that movement of the coil inresponse to signaling impulses may serve partly to remove the coil fromthe influence of the field, and the response for a large coil movementis materially lessened. In my two coil arrangement, this effect isnicely overcome, for as one coil moves out of the field, the other canmove into the field. Furthermore, the effect of the coils on the airactuator is cumulative, to 50 produce a push-pull result.

It is often desirable to provide separate speakers adapted faithfully toreproduce different reg isters in the range of audible frequencies. Forexample, a horn and cone are often used together, the hornbeing bestadapted to reproduce the higher frequencies and the cone to reproducethe lower frequencies. It is another object of my invention to provide asingle unit in which the low and high register elements are embodied ina compact and inexpensive manner.

This compact arrangement is rendered possible by so arranging the conethat it may serve as the mouth of a, horn having converging passagewaysleading to the cone.

My invention possesses many other advantages, and has other objectswhich may be made more easily apparent from a consideration of severalembodiments of my invention. For this purpose I have shown a few formsin the drawing accompanying and forming part of the presentspecification. I shall now proceed to describe these forms in detail,which illustrate the general principles of my invention; but it is to beunderstood that this detailed description is not to be taken in alimiting sense, since the scope of my invention is best defined by theappended claims.

Referring to the drawing:

Figure 1 is a sectional view, mainly diagrammatic, of a loud speakerunit embodying my invention;

Fig. 2 is a diagram showing the manner in which the two sections of themovable coil used in my device are energized; and

Fig. 3 is a diagram of that form of the invention in which the deviceembodies the characteristic both of a horn and of a large diaphragm,such as a cone.

In Fig. 1, I show a field coil 11 in diagrammatic fashion only. It isshown as disposed on a tubular magnetic member 12. This member has aninternal flange 13, forming a large central aperture at one end. It canbe further provided with an external flange 14 at the opposite end,against which one end of coil 11 can rest. The exterior of coil 11 iscovered by a tubular magnetic casing 15 fastened to flange 14. At itsother end, this casing is provided with an annular pole piece 16 formingan aperture of substantially the same size as flange 13, but overlyingit.

A short core piece 17 is held centrally of both flange 13 and pole piece16, as by the aid of a non-magnetic bridging member 18. This bridge 18can be fastened in tube 12, and a screw 19 passing through it can serveto hold the piece 1'7 firmly in centered or central relation to themembers 13 and 16 1 It is apparent that if, say, the pole piece 16 formsa north pole, the inner edge of flange 13 must form a south pole. Thecore 1'7 at that portion opposite the inner edgeof pole piece 16 has asouth pole induced thereby; and that portion opposite flange 13 has anorth pole induced thereby. The course of the lines of force through thecore 1'7 is shown by arrows 19'. Thus it is seen that two narrow airgaps are formed; in one, the lines radiate outwardly from a north pole(opposite flange 13); and in the other, the lines converge inwardly to asouth pole (opposite piece 16). 1

Before proceeding with a description of the moving parts of themechanism, attention is directed to the fact that a large interiorcooling surface is presented by the interior of tube 12. Consequentlythe heat energy lost in coil 11 can be easily dissipated without dangerof excessive temperature rise.

Cooperating with the two narrow annular air gaps, are a pair of coils20, 21, supported on a thintube 22 attached to a cone 23. This cone canbe fastened in any appropriate manner at its edges, whereby the wholemovable structure is constrained for axial movement. Then as these coilsare axially moved, the cone 23 is actuated to set up corresponding soundwaves. In order that these coils have a cumulative effect on the cone,they must of course carry currents that circulate in opposite directionsbecause the lines of force in the two air gaps extend in differentdirections. Thus for coil 20, influenced by the gap formed by flange 13,currents must be supplied that circulate, say, in a clockwise direction;while for coil 21, influenced by the gap formed by annular member 16,currents must be supplied that circulate in a counterclockwisedirection. The coils can be supplied from a circuit 24 (Fig. 2) thatcarries the signaling impulses by having one terminal of the circuitconnecting to a common point 25 for both coils; and the other terminalconnects to the outer terminals of both coils, thus providing a parallelconnection for the coils; and if the coils are wound in the samedirection on tube 22, the currents will then circulate in oppositedirections. The magnetic effects of coils 20, 21 are indicated by arrows26, 27, and since both coils are of equivalent number of turns, thesetwo effects cancel each other. There is thus no magnetic reaction, dueto these coils on the core.

Preferably, I arrange coils 20 and 21 so as to.

be not quite centrally disposed in the gaps when these coils areunexcited; coil 20, say, has its medial line passing to the'right of themedial line of flange 13; and the coil 21 has its medial line passing tothe left of the medial line of annular member 16. In this way, whenthese coils are pole pieces 29, 30, one at each end. A central core 31passes entirely through the coil 28, and forms with the pieces 29, 30, apair of gaps that function in a manner analogous to the form of Fig. 1.Coil 32, at the right hand side of the device, is connected directly toa cone or large diaphragm 33. Coil 34, at the left hand end, issupported on a cup-like member 35, the end or which forms the centerportion of a diaphragm 36, fastened to a stationary support at itsedges.

The movement of coil 34 actuates this diaphragm,

and the sound waves caused thereby can be led through a divergingcentral opening 37 in the core 31 and finally out through the cone 33.

It is evident that cone 33 serves not only as a diaphragm air actuator,but also to lead the sound waves out from another, smaller diaphragm.The coils 32, 34, can be connected either in parallel or in series to acommon source of signaling currents. Diaphragm 33 correctly reproducesthe lower notes, while the smaller diaphragm 35-36 correctly reproducesthe higher notes. Some of the advantages of the structure of Fig. 1 arealso present; there is an internal radiating surface, and two movingcoils are used.

I claim: v

1. In a dynamic signaling device, a core, a pair of annular pole pieces,one at each end of the core to form annular gaps, a movable coil in eachgap, and diaphragms operatively associated respectively with eachmovable coil, said core having a tapering aperture therethrough forleading sound waves through the core.

2. The'combination as set forth in claim 1, in which the'largerdiaphragm or cone is in the form of a large mouthpiece forming anextension for the aperture in the core.

3. In a dynamic loud speaker, a pair of dynamic coils axially displacedfrom each other, a core passing through both coils, an air actuatoradapted to reproduce the lower register of sound waves, operated by oneof the coils, and an air actuator adapted to reproduce the higherregister, operated by the other coil, the core having an axial apertureforming with the low register actuator, a horn-like air passage from thehigher register actuator.

4. A sound reproducing system comprising in combination a loud speakingreceiver having a diaphragm and a horn amplifier and a second loudspeaking receiver having a free radiating diaphragm, the diaphragm ofsaid second receiver having a central opening substantially equal to theopening of the horn mouth of saidv first receiver and being locatedcircumferentially around the mouth of said horn.

5. In combination a moving coil loud speaker having a horn radiator, is.second moving coil loud speaker having a free radiating diaphragm, and acommon field magnet system for the moving coilsof both of said loudspeakers.

6. In combination, a loud speaking receiver having a diaphragm and ahorn radiator, and a second loud speaker comprising a diaphragm, adriving coil mounted on said last recited diaphragm, and a cylindricalshell type magnet providing a magnetic field for said driving coil, saidmagnet having a hollow central core the interior wall of which is formedto provide the horn for said first loud speaker.

7. A sound reproducing system in accordance v with claim 6 in which thediaphragm of the second loud speaker is a free radiating cone havinga'central opening and is mounted circumferentially of the horn openingof the first loud speaker.

8. In combination, a loud speaking receiver having a diaphragm and ahorn radiator, and a second loud speaking receiver comprising a freeradiating diaphragm, a driving coil mounted on said free radiatingdiaphragm, and a cylindrical. shell type magnet providing amagnetic'fleld for said coil, the horn of said first loud speaker beinglocated centrally and coaxially' within said magnet and said freeradiating diaphragm having a central opening substantially coincidingwith the horn mouth.

HERMAN J. FANGER.

